“She was very set in her ways,” said a sister in Mexico, Ely, who had tried to persuade Ms. Martínez not to leave. “Once she decided to do something, there was no stopping her.”

The Border Patrol has reported a large drop in the number of illegal immigrants apprehended at the border with Mexico this year, the consequence, the agency says, of additional agents and the presence of National Guard troops. Yet the number of migrants dying while trying to cross here in Pima County is on pace to set a record, according to the county medical examiner.

Pima County, which includes the Tucson area, is one of the busiest areas for illegal crossings along the 2,000-mile border. The medical examiner’s office handled 177 deaths of border crossers in the first eight months of this year, compared with 139 over the same period last year and 157 in 2005, the year the most such deaths were registered.

The death of Ms. Martínez in July illustrates a primary reason that immigration scholars, the Border Patrol and government officials in the United States and Mexico believe people continue dying at such high rates: As they increasingly avoid heavily patrolled urban areas, they cross with little or no knowledge of the desert, whose heat, insects, wildlife and rugged terrain make it some of the most inhospitable terrain on the planet.

Like Ms. Martínez, who had worked cleaning houses in Mexico, many crossers arrive from central and southern Mexico, which is cooler and wetter than Arizona and where people are less familiar with the desert and its perils.

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Kelly Kirby, a Border Patrol agent, walking to the site where he found Ms. Martínezs body.Credit
Monica Almeida/The New York Times

Before entering the Sonoran Desert, she had completed a three-day trip to the Mexican side of the border, part of the marathon trek from her lush, verdant subtropical village of Tepetlán, a four-hour drive northeast from Mexico City in Veracruz state.

Her cousin, Mr. Díaz, said they stayed in a room at the border with 15 other crossers and were each given two cans of tuna, a bag of tortilla chips, and six liters of water — a gallon and a half — by a smuggler before setting off for the desert.

The growing death toll here in recent years follows a Border Patrol clampdown in California and Texas. The goal was to drive migrant traffic away from cities like San Diego and El Paso and into the remote desert on the assumption it would act as a deterrent. But while there is no way of knowing its overall effect, the strategy is serving at least in part as a funnel for untold numbers of migrants.

The Government Accountability Office, in a report last year that analyzed Border Patrol statistics, said the annual number of reported deaths of border crossers doubled to 472 between 1995 and 2005, with the majority of those deaths in the desert near Tucson. The report suggested the agency has undercounted deaths because of inconsistent classification.

Border Patrol officials say that as the agency continues to add agents, as recently authorized by Congress, they will be better able to patrol the toughest areas of the Sonoran Desert. It said commanders recently met to finalize better methods to count migrant deaths.

“We are well aware of the perils of crossing the desert,” said Lloyd Easterling, an agency spokesman. “That’s why we are trying to get people to places to deter people from crossing to begin with.”

At the Mexican consulate in Tucson, a map is adorned with yellow and blue pieces of tape, for females and males, marking where migrants have died. Ms. Martínez is yellow No. 114.

Jerónimo García Ceballos, a consular official, maintains the map and devotes much of his work to identifying the dead and arranging for their bodies to be returned to Mexico.

Mr. García’s office is adorned with posters with slogans like “Don’t leave your life in the desert; your family asks you not to,” an example of the public service announcements that both Mexico and the United States Border Patrol have used along known migrant trails.

Ms. Martinez had telephoned home as she hopscotched across Mexico with Mr. Díaz. They rode in a smuggler’s sport utility vehicle to Xalapa, took a bus to Mexico City and then another, three-day bus trip to Altar, a ragged town that is a major staging area for migrants 50 miles south of the border.

“I would tell her it’s not too late to come back, I would work to pay off the smuggler,” said Ms. Martínez’s father, Vicente Martínez Ortega, recalling his telephone conversations with her along the way.

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From Altar, they were driven toward the border in a van, Mr. Díaz said, and once they got close, they began walking. They headed along a known smuggling route toward Route 86 in Arizona, where migrants are often picked up and eventually carried to points across the United States.

Mr. Díaz said they were assured it would be a day or so of walking but Border Patrol agents say from the border to Route 86 is more like a three- or four-day walk.

Ms. Martínez’s last call home came a couple of days before she died. “She said, ‘Daddy, I’ve reached the border,’ ” Mr. Martínez said.

Tepetlán, a village of 1,800 people on a high plateau in the southeastern flanks of the Sierra Madre Oriental, has shrunk in population in recent years as scores of its citizens head “al otro lado,” to the other side, as the United States is called.

Family and friends there said Ms. Martínez had chosen to believe, like many others who try to cross, that nothing ill would come to her.

Her younger brother had successfully made a similar journey eight months before and found work at a factory in Georgia, but said he had told his sister of the exhausting, broiling march in the desert and warned her not to do it.

“I told her work here is hard and sometimes there isn’t any,” her brother Vicente, 24, said in a telephone interview from Georgia, where his job helps support his parents, wife and two young children in Tepetlán. “But she thought everything would come out all right.”

Her father had crossed several years ago in San Diego, scrambling away from Border Patrol agents tracking him and his group with helicopters and floodlights. He found field work in California and Nebraska and sold ice cream pops in Chicago before tiring of the climate and intermittent work and returning home to harvest coffee in Tepetlán.

Mr. Díaz, too, had made the trek just a year before, but said he was caught by the Border Patrol and immediately deported.

The Martínez family lives modestly in a two-room house in Tepetlán. It sits on an unpaved road where rural scenes naturally unfold: men riding burros, boys playing with a captured armadillo, and fish and fruit vendors hawking wares from battered pickup trucks.

Ms. Martínez had worked cleaning houses in Veracruz and at the airport there for a year but she found it hard to make enough money to care for her children, ages 6 to 13.

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Her personal life, too, had been turbulent for years. Family members describe her as somewhat rebellious and headstrong.

She had dropped out of high school at 14, was married and pregnant by 15 and had left the father of her four children last year, after several fights.

She had remarried and was looking for ways to make big money for a new house.

Ms. Martínez had heard that Mr. Díaz was planning to make another try, through a smuggler who was a distant relative, and borrowed money from a lender in town. The cost would be $3,000, half paid up front, half after a successful crossing.

But it was not. Around 11 a.m. on July 6, Border Patrol Agent Kelly Kirby got a call about a young migrant reporting his cousin possibly dead in the desert. Every time a call about a migrant in distress comes in, Agent Kirby says he hopes for the best but knows to expect the worst.

Mr. Díaz said Ms. Martínez died just before sunset the night before. He cried and was scared, he said, and built a fire, hoping to be spotted.

He set off in the morning to find help, eventually flagging down a passing Border Patrol agent.

Agent Kirby responded and with Mr. Díaz’s help quickly found Ms. Martínez.

She was wearing jeans and a blouse. Foam around her mouth was evidence of a seizure. Though she had only walked about a day and a half, her physical condition and the insufficient water and food she had consumed made her susceptible to a desert death.

“She did about as much as she could to not make it,” Agent Kirby said.

When Ms. Martínez’s body was returned to Tepetlán, the coffin was brought into the house for a wake. Her father opened the lid and looked at his daughter’s face.

“I had to look, to see her,” Mr. Martínez said.

Mr. Martínez, with the help of a friend who is a mason, is completing work on a tomb, which includes a sculpture of the town church where Ms. Martínez’s mother took her for a blessing before she left for the United States.

Watching the work on the tomb from a distance one afternoon in late August, Mr. Díaz spoke of his life since his cousin’s death and the possibility of another attempt to cross.

“Not right now,” he said, “but who knows, later on?”

A version of this article appears in print on , on page A1 of the New York edition with the headline: At U.S. Border, Desert Takes A Rising Toll. Order Reprints|Today's Paper|Subscribe